Japanese Patent Laid-Open Publication No. 2005-112173 (JP 2005-112173 A) teaches an automobile front body structure provided with a front side frame that extends in the longitudinal direction of the vehicle body, and a lower frame that is disposed on the exterior thereof and extends to the edge of a wheel housing. The front body structure will be described with reference to FIG. 8 hereof. FIG. 8 is a top plan view showing a portion of the front body structure.
A front body structure 200 has a front side frame 201 that extends in the longitudinal direction of the vehicle. The rear end of the front side frame 201 is fixed to the bottom edge of a wheel housing 202. The front end 201a of the front side frame 201 is provided with an impact absorbing member 203.
A front pillar (not shown) is disposed above the rear part of the front side frame 201. A lower frame 204 extends from the bottom end of the front pillar toward the front of the vehicle body. The lower frame 204 is disposed on the outside of the front side frame 201, as viewed in the width direction of the vehicle.
The substantially central part of the lower frame 204 is formed so as to reach the upper surface of the wheel housing 202. The front end 204a of the lower frame 204 is connected to the front end 201a of the front side frame 201 via a connecting member 206.
The front end 204a of the lower frame 204 and the front end 201a of the front side frame 201 extend parallel to each other. Therefore, the connecting member 206 must be disposed so as to be orthogonal to the front side frame 201 and the lower frame 204 in order to connect the front ends 201a, 204a via the connecting member 206.
When a relatively small load Fa is applied to the front surface of the impact absorbing member 203 in the front body structure 200, as indicated by the arrow, a portion of the load Fa is absorbed by the impact absorbing member 203. The remainder of the load is dispersed as loads Fb and Fc to the front side frame 201 and the lower frame 204 via the connecting member 206.
The connecting member 206 is disposed so as to be orthogonal to the front side frame 201 and the lower frame 204. The transmission direction varies considerably, as indicated by the arrow, when the load Fc is transmitted from the front side frame 201 to the connecting member 206. The transmission direction varies considerably, as indicated by the arrow, when the load Fc that has been transmitted to the connecting member 206 is transmitted further to the lower frame 204 from the connecting member 206. Therefore, the remainder of the load must be temporarily supported by the front side frame 201, and the rigidity of the front side frame 201 is set high.
Setting the rigidity of the front side frame 201 to a high level is thus an obstacle to reducing the weight of the front body structure 200, and there is room for improvement in this respect.